Two-dimensional transition metal carbides and carbonitrides, so-called MXenes, is produced by selective etching of atomically thin metal layers from MAX phases. The latter is a large family (>70 members) with composition of Mn+1AXn; M is an early transition metal carbide, A is one of groups IIIA and IVA, X is carbon and/or nitrogen, and n = 1, 2, or 3. MXenes morphology, chemical versatility, and excellent conductivity suggested them to be excellent materials for electrochemical energy storage systems. Herein, an overview on the synthesis of MAX phases and MXenes will be discussed. Also, the recent progress in the use of MXenes in electrochemical energy storage systems, including Li-ion batteries, will be presented.